In a self-organizing wireless network, network nodes (e.g., devices on the network) cooperate to form routes and deliver data packets generated by the nodes to the packets' intended destinations. When the physical distance between the source of a data packet and its destination is longer than the radio transmission range of nodes corresponding to the source and destination, delivery of the packet will require one or more relays (i.e., hops) between the source and destination nodes.
It is well known that a homogeneous network with a flat structure is highly self-configurable in the sense that nodes can be randomly deployed in a given space without following any hierarchy. Without a hierarchy, every node in a homogeneous network relies on its neighboring nodes within a wireless transmission range to forward outgoing data packets and to deliver incoming data packets.
Whenever a node of a homogeneous network is not a data originator, the node prepares to function as a router and actively listens to a communication channel so that it can capture data transmitted by its neighboring nodes and forward the data along a path to the data's destination (if the node itself is not the destination). All nodes in a homogeneous network continuously operate in either a “transmit” mode or a “receive” mode, rarely going into a power-saving “sleep” mode. As a result, power efficiency in a homogeneous network is often limited, since all nodes in the network are constantly activated in the receive mode, even when the communication channel is quiet.
In contrast to a homogeneous network, a heterogeneous network has a well-defined, rigid hierarchy, which explicitly specifies the function of every node in the network. Only certain nodes in a heterogeneous network that have sufficient power resources can operate with a high duty cycle and, therefore, provide routing capabilities.
Nodes with limited power sources, such as batteries, can operate with a much lower duty cycle, since they do not need to provide routing functions. When such nodes only acquire data from devices that they are connected to, and serve as data originators in the network, such nodes represent endpoint devices in the network hierarchy. These endpoint devices become activated only when they originate data, which occurs on a periodic or event-driven basis. Since such nodes do not have routing responsibilities, they go into a power-saving (e.g., low-power) mode when not transmitting or receiving data.
Thus, it is evident that a heterogeneous network allows endpoint devices to operate with a power efficiency that is much higher than the power efficiency of uniform nodes in a homogeneous network. In most heterogeneous networks, all data is directed toward one or a few nodes designated as base stations. In a heterogeneous network, base stations are pinnacles of the hierarchy. All other nodes are members of the network with a certain rank in the hierarchy. A device's rank depends on various factors, such as relative distance from the base stations, power resources, and radio link reliability.
One drawback of a conventional heterogeneous network is that every member node has a limited and defined role in the hierarchy. Without the capability of adapting router distribution to changing conditions, such a network will not be able to handle changing conditions effectively. For instance, when traffic is relatively low, the network can be overly populated with routers that operate with an unnecessarily high duty cycle, leading to relatively low power efficiency.